The present invention relates to an exhaust emission control apparatus of an internal combustion engine, and particularly to such a control apparatus of an internal combustion engine employing an intake air flow control valve actuator to which voltage is applied from a car storage battery to drive an intake air flow control valve.
An airflow control valve is generally used in induction systems of internal combustion engines. In an intake system disclosed in Japanese Patent Provisional Publication No. 63-143349, an intake air quantity control valve such as a butterfly valve is provided in an intake air passage to adjust a quantity of intake air entering a combustion chamber, and during engine cranking the butterfly valve is driven in a direction decreasing the intake-air quantity and kept at its closed position, so as to prevent knocking during the starting period. In this case, the butterfly valve is returned to its full-open position with a delay time after complete explosion. In an internal combustion engine disclosed in Japanese Patent Provisional Publication No. 8-109836, an intake air flow control valve such as a butterfly valve is provided in an intake-air passage between a throttle valve and a fuel injection valve, and in order to prevent icing (occurring owing to freezing of condensed water adhered to the inner wall surface of the intake-air passage) and to rapidly drive the butterfly valve during the engine starting period, the butterfly valve is held temporarily at an intermediate valve-opening position at the time when the engine is stopped. During the engine cranking (or when the engine is restarted), the butterfly valve is driven to its closed position to constrict airflow entering the combustion chamber, and to increase the negative pressure (boost), thereby promoting atomization of fuel spray injected from the injection valve for good combustion.
When a valve actuator having a driving connection with the previously-noted intake air quantity control valve (butterfly valve) or the previously-noted intake air flow control valve (butterfly valve) is an electric actuator which is electrically operated by means of an electric power source such as a storage battery, there is a possibility that the electric valve actuator cannot be smoothly driven and thus the butterfly valve cannot be smoothly controlled to a desired valve opening due to a momentary drop in battery voltage during cranking, in particular during engine starting in cold weather (see FIG. 6). As shown in FIG. 6, during cold-start operation, the battery voltage varies remarkably. That is, as soon as the engine is brought into the cranking state by turning the starter switch ON, a large amount of current flows into the starter motor and as a result the battery voltage temporarily reduces to below approximately 8 volts. Thereafter, when the complete explosion is assured and thus the starter switch is turned off to terminate the engine-cranking operating mode, the battery voltage rises up to a specified voltage level (approximately 14 volts). A step motor is often used as an electric valve actuator. As is generally known, the battery voltage, which is less than a predetermined voltage level (e.g., 10 volts) below the specified voltage level (approximately 14 volts), never assures operation of the step motor. Assuming that the lowest voltage that assures operation of the step motor is defined as a step-motor operating voltage limit (or a step-motor operation assurance voltage), there is an increased tendency for the battery voltage to become less than the operating voltage limit during engine cranking at the starting period. In such a case, even when a command signal or a step-motor drive signal is output to the step motor, the butterfly valve (serving as the intake air quantity control valve or the intake air flow control valve) cannot be accurately driven to the desired valve opening.
Accordingly, it is an object of the invention to provide an exhaust emission control apparatus of an engine, which avoids the aforementioned disadvantages.
It is another object of the invention to provide an exhaust emission control apparatus of an engine employing an intake air flow control valve in an induction system, which avoids the control accuracy of the intake air flow control valve from deteriorating during engine cranking at a starting period, in particular during cold-start operation.
In order to accomplish the aforementioned and other objects of the present invention, an exhaust emission control apparatus of an internal combustion engine, comprises a fuel injector which injects fuel into an intake air passage, an intake air flow control valve which controls intake air flow exerting an influence upon a behavior of fuel injected from the fuel injector, a valve actuator which is electrically operated by a storage battery serving as an electric power source to drive the intake air flow control valve, and a control unit connected electrically to at least the valve actuator for controlling an opening of the intake air flow control valve, the control unit having a processor programmed to perform the following, controlling the opening of the intake air flow control valve to a predetermined intermediate valve opening by the valve actuator during an engine stopping period, and holding the intake air flow control valve at the predetermined intermediate valve opening, by inhibiting operation of the valve actuator during an engine-cranking operating mode at a starting period.
According to another aspect of the invention, an internal combustion engine comprises fuel-injection means for injecting fuel into an intake air passage, valve means for controlling intake air flow exerting an influence upon a behavior of fuel injected from the fuel-injection means, drive means electrically operated by a storage battery serving as an electric power source for driving the valve means, and a control unit connected electrically to at least the drive means and the storage battery for controlling an opening of the valve means, the control unit comprising means for controlling the opening of the valve means to a predetermined intermediate valve opening by the drive means during an engine stopping period, and means for holding the valve means at the predetermined intermediate valve opening to which the valve means has been driven in advance during the engine stopping period, by inhibiting operation of the drive means during an engine-cranking operating mode at a starting period.
According to a further aspect of the invention, a method of controlling exhaust emissions emitted from an internal combustion engine with a fuel injector injecting fuel into an intake air passage, an intake air flow control valve, and an electric valve actuator electrically operated by a storage battery serving as an electric power source to drive the intake air flow control valve, the method comprises controlling intake air flow exerting an influence upon a behavior of fuel injected from the fuel injector, controlling the opening of the intake air flow control valve to a predetermined intermediate valve opening by the electric valve actuator during an engine stopping period, and holding the intake air flow control valve at the predetermined intermediate valve opening, by inhibiting operation of the electric valve actuator during an engine-cranking operating mode at a starting period. It is preferable that the method may further comprises inhibiting the operation of the valve actuator for a predetermined delay-time duration from a time when the engine-cranking operating mode has been completed, and enabling the operation of the valve actuator to drive the air flow control valve toward a valve opening that reduces a density of unburned hydrocarbons emissions during engine idling after expiration of the predetermined delay-time duration.